The present invention relates to power line carrier systems and, more particularly, to a novel method of, and novel apparatus for, driving the secondary windings of a distribution transformer to insert power line carrier signals onto the primary winding thereof, for transmission over a power distribution network.
Many different systems are known for communication of information utilizing power lines as the transmission media. In a typical system, information may be transmitted from a central facility for reception at a remote location, or may be transmitted from the remote location for reception at the central facility. In the latter case, the remotely located transmitter is typically coupled to the secondary winding of a distribution transformer and the remote location transmitter must provide sufficient signal power for providing a power line carrier signal of significant amplitude upon the conductors of the power distribution network connected between the distribution transformer primary winding and the central location. Due to the large admittances of power-consuming loads connected to the power transformer secondary winding, a relatively great amount of signal power must be supplied to the distribution transformer secondary winding in order to cause transmission of a power line carrier (PLC) signal with a sufficiently high signal-to-noise ratio to assure reliable detection at the central facility. If a conventional transmitter is utilized to provide this relatively large signal power, the transmitter and its associated power supply (which must be relatively large in size and relatively stable and ripple-free) will be relatively expensive. Accordingly, any method capable of increasing the signaling current coupled to the power line, without requiring a transmitter of increased power output, and also overcoming the need for the stable, ripple-free power supply, is desirable in terms of cost-effectiveness.